1. Field of the Invention
This invention relates to silicone oligomers useful as coupling agents for curable compositions, for instance free-radically curable filler-organic elastomeric polymer compositions having special application as insulation coatings, to compositions employing the oligomers, and to cured products obtained therefrom.
2. Description of the Prior Art
A substantial amount of research has been performed heretofore in connection with the treatment of fillers or reinforcing agents for the purpose of improving physical or mechanical properties of plastics, resins or rubbers reinforced with the filler. Much of this research has centered on the pretreatment of glass fiber reinforcement materials for resins and rubbers. For example, U.S. Pat. No. 3,702,783 describes the application as a size to glass fibers of a blend of 3-glycidoxypropyltrirethoxysilane and methyltrimethoxysilane. U.S. Pat. No. 3,816,235 discloses a size composition for the treatment of glass fibers wherein the size composition contains a blend of aminoalkyltriethoxysilane and methyltriethoxysilane. U.S. Pat. No. 3,944,707 discloses the use as a size for glass fiber reinforcement for plastics, blends of vinyl silane or vinyl siloxanes and a beta-haloalkoxysilane. Similarly, U.S. Pat. No. 3,993,837 discloses glass fiber size compositions containing blends of epoxyalkylsilane or siloxane and a beta-haloalkoxysilane.
U.S. Pat. No. 4,049,865 discloses glass fiber size compositions containing a blend of an aminoalkylsilane and a vinyl silane. U.S. Pat. No. 4,130,677 discloses the sizing of glass bottle surfaces with am aminoalkylsilane. None of these patents disclose or remotely suggest the use of blends of an ethylenicaly unsaturated silane having at least 1 silicon bonded hydroxy or alkoxy group and an organosiloxane oligomer having at least one silicon bonded hydroxy or alkoxy group reactive with the inorganic substrate as an integral coupling composition for improving mechanical and electrical properties by mixing with an organic elastomer, a filler and peroxide followed by curing.
Martens et al, U.S. Pat. No. 3,148,169, discloses the pretreatment of clay filler with a silicone fluid to coat the clay particles to impart a hydrophobic character to the clay and to mask the acidic nature of the clay so that peroxides later used as crosslinking agents are not deactivated.
Pickwell et al, U.S. Pat. No. 4,550,056, describes electrical cables comprising a conductor and a coating of insulation on the conductor, the coating comprising a cured composition of
(1) an organic elastomer; PA1 (2) an inorganic filler; PA1 (3) a coupling composition comprising (a) an ethylenically unsaturated silane, having bonded to silicon, at least one hydroxy group and/or alkoxy group; (b) a methyl ethoxy siloxane oligomer fluid; and (c) a methyl vinyl siloxane oligomer fluid. PA1 each R is selected individually from the group consisting of B, R.sup.1,--OR.sup.2, R.sup.3 and R.sup.4 ; B is an organosilyl functional group bridged to the Si atom of the siloxane oligomer backbone by an Si--C bond; each R.sup.1 is independently a saturated or aromatic hydrocarbon group of 1 to 16 carbon atoms; each R.sup.2 is independently a group as defined for R.sup.1 or an acyl group; and each R.sup.3 is independently a monovalent organic radical containing an aliphatically unsaturated hydrocarbon group and each R.sup.4 is a monovalent organic radical linked to the Si atom of the siloxane oligomer backbone by an Si--C bond, which does not include an aliphatically unsaturated hydrocarbon group and which has thereon one or more members of the group selected from ether, polyether, ester, polyester, carbamate, polyurethane, isocyanurate, thioether, polysulfide, blocked mercaptan, amide, cyano and oximato groups; with the provisos that at least one R is a B, at least one quarter of all R groups are --OR.sup.2, and at least one silicon atom of the oligomer has an R.sup.3 group thereon; m=2 to 10; n=0 to 20; o=0 to 20; and p=0 to 10. PA1 (1) an organic polymer curable by a free radical mechanism; PA1 (2) an inorganic filler; PA1 (3) a siloxane oligomer as described above.
Rykowski, U.S. Pat. No. 4,179,537, discloses blends of an organofunctional silane, e.g., vinyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes, vinyltrihalosilanes and the like with a non-organofunctional silane, e.g., alkyltrialkoxysilanes, and the incorporation of such blends into organic resins, e.g., EPDM rubber for improving the adhesion between inorganic substrates such as clay fillers and the resin. This patent fails to disclose, teach or suggest the incorporation of siloxane oligomers in the coupling composition and suggests that the presence of siloxane oligomers in the resin-filler system could have a detrimental effect on coupling efficiency (col. 4, lines 54-63).
Use of silanes having silicon-bonded 2-methoxyethoxy groups as coupling agents, e.g., vinyl-tris-(2-methoxyethoxy)silane (col. 2, lines 44-47) is also described in U.S. Pat. No. 4,179,537. Vinyl-tris-(2-methoxyethoxy)silane, has been used industrially for many years as a coupling additive in mineral-filled EPM and EPDM wire and cable insulations. EPM is an ASTM designation for copolymers or ethylene and propylene; EPDM is a terpolymer of ethylene, propylene and a diene monomer such as ethylidene norbornene or 1,4 hexadiene. Vinyl-tris-(2-methoxyethoxy)silane has been extensively used heretofore because it provides a unique balance of elastomer reinforcement and the degree of wet electrical stability required. However, it releases 2-methoxyethanol as a hydrolysis by-product when it is used and, unfortunately, 2-methoxyethanol is now being studied as a suspected teratogen. Consequently coupling agent products based on vinyl-tris-(2-methoxyethoxy)silane are now facing continuing replacement pressure in the marketplace.
Commercial products used as coupling agents in elastomer/filler compositions include cohydrolysis products of dimethyl and vinylmethylchlorosilanes which are used as a filler hydrophobe treatment on calcined clays. Such products however, have a relatively high cost due to the high cost of vinylmethyldichlorosilane. Reducing the vinylmethyldichlorosilane content thereof gives inferior performance in wire cable insulation applications.
U.S. Pat. No. 4,950,779, Wengrovius, et al. (General Electric), describes mixtures comprising cyclic, linear and branched alkoxy functional silicone oligomers produced by condensation of organotrialkoxysilanes, such as methyltrimethoxysilane and vinyltrimethoxysilane, using formic acid, optionally with a strong acid catalyst.
U.S. Pat. No. 5,298,998, Horn, et al. (Huls), describes mixtures of linear and cyclic alkoxy functional silicone oligomers produced from vinyltrialkoxysilanes using hydrogen chloride catalyst and water.
U.S. Pat. No. 5,210,168, Bergstrom, et al. (Dow Corning), describes alkoxy functional silicone oligomer mixtures produced from organotrialkoxysilanes using a carboxylic acid, such as formic acid, and a strong acid catalyst.
In copending U.S. patent application Ser. No. 09/062,047, filed Apr. 17, 1998, incorporated herein by reference, there are described novel alkoxy functional silicone oligomers having alkoxysilylalkyl substituents on a backbone silicon atom. Such oligomers may be produced, from vinylalkoxysiloxane oligomers by hydrosilation with an alkoxyhydridosilane; by hydrosilating a vinylalkoxysilane with a hydridoalkoxy silicone oligomer; or by condensation of a bis-alkoxysilane having silicon atoms joined by other than an Si--O bond, optionally with other alkoxysilanes. Such oligomers are disclosed to be useful as coatings or adhesive, or additives therefore.